Snowshoe Hare, Lepus americanus, is a species of hare found in North America, primarily in the northern boreal forests. It is a keystone prey species and can experience fluctions in population density. This analysis explores these fluctuations in a population of snowshoe hares in the Bonanza Creek Experimental Forest from 1999 to 2012. Data was collected by Kielland et al. from 1999 to 2012.
Citation:
Kielland K., F. S. Chapin, R. W. Ruess. 2017. Snowshoe hare physical data in Bonanza Creek Experimental Forest: 1999-Present. Environmental Data Initiative. https://doi.org/10.6073/pasta/03dce4856d79b91557d8e6ce2cbcdc14.
##### Wrangle the data to inclue variables of choice: sex and weight of snowshoe hares#####
### Total observations = 3380 (including all sex and NA values)
### Observations with KNOWN sex = 2628 (includes M, F, m, f)
#### Clean up DATE and extract YEAR
snowshoe$date = as.Date(snowshoe$date, "%m/%d/%y")
snowshoe$year = as.numeric(format(snowshoe$date, "%Y"))
## Get total abundance for snowshoe hare observations by counting up total observations by year
## Filtered out observations where the sex was unknown ******
# Get counts by year/sex
abundance <- snowshoe %>%
select(year, sex, weight) %>%
mutate(sex = case_when(sex =="M" ~ "Male",
sex == "F" ~ "Female",
sex == "f" ~ "Female",
sex == "m" ~ "Male"
)) %>%
group_by(year, sex) %>%
drop_na() %>%
tally()
# Total observations for male/female with weights
abundance_weights <- snowshoe %>%
select(year, sex, weight) %>%
mutate(sex = case_when(sex =="M" ~ "Male",
sex == "F" ~ "Female",
sex == "f" ~ "Female",
sex == "m" ~ "Male"
)) %>%
drop_na()
# Plot Total Abundance
abundance_plotly <- ggplot(abundance, aes(x = year, y = n)) +
geom_line(aes(color = sex, text = n)) +
ggtitle("Population Density of Snowshoe Hares in the \n Bonanza Creek Experimental Forest, 1999-2012") +
theme_classic() +
xlab("Year") +
ylab("Number of Snowshoe Hares Recorded") +
theme(plot.title=element_text(hjust=0.5)) +
labs(color = "Sex")
## Warning: Ignoring unknown aesthetics: text
abundance_plotly <- ggplotly(abundance_plotly)
abundance_plotly
Figure 1. Population Density of Snowshoe Hares, 1999-2012. Capture and re-capture studies were conducted on a snowshoe hare population in Bonanza Creek Experimental forest between 1999 and 2012. Data was collected on the sex, weight, and highfeet length. This graph only shows data for snowshoe hares where the sex was confirmed. Total observations during the study period were n = 3380. Observations including hares with known sex is n = 2628.
There is a significant increase in abundance between 1998 and 1999 for both males and females, and then a subsequent decrease between 1999 and 2002. Between 2002 and 2009, both male and female snowshoe hares again increase in abundance and then drop off again between 2009 and 2012. Some of the driving factors for these fluctuations could be predation or changes in habitat, such as vegetation cover.
### Create summary table for abundance
# total observations for male and female by year
abundance_table <- kable(abundance,
col.names = c("Year", "Sex", "Count")) %>%
kable_styling(bootstrap_options = c("striped", "hover"),
full_width = F,
position = "float_right",
fixed_thead = T
) %>%
scroll_box(width = "200px", height = "300px")
abundance_table
| Year | Sex | Count |
|---|---|---|
| 1998 | Female | 15 |
| 1998 | Male | 18 |
| 1999 | Female | 163 |
| 1999 | Male | 185 |
| 2000 | Female | 121 |
| 2000 | Male | 107 |
| 2001 | Female | 38 |
| 2001 | Male | 57 |
| 2002 | Female | 11 |
| 2002 | Male | 17 |
| 2003 | Female | 34 |
| 2003 | Male | 23 |
| 2004 | Female | 45 |
| 2004 | Male | 29 |
| 2005 | Female | 103 |
| 2005 | Male | 58 |
| 2006 | Female | 78 |
| 2006 | Male | 33 |
| 2007 | Female | 132 |
| 2007 | Male | 58 |
| 2008 | Female | 164 |
| 2008 | Male | 133 |
| 2009 | Female | 247 |
| 2009 | Male | 185 |
| 2010 | Female | 207 |
| 2010 | Male | 113 |
| 2011 | Female | 129 |
| 2011 | Male | 80 |
| 2012 | Female | 24 |
| 2012 | Male | 21 |
Table 1. Abundance by year and sex. Population counts by year and sex. This dataset only shows observations for hares where sex was known.
hare_weights <- ggplot(abundance_weights, aes(x = year, y = weight)) +
geom_point(aes(color = sex)) +
xlab("Year") +
ylab("Weight (g)") +
facet_wrap(~sex) +
labs(color = "Sex") +
theme_bw()
hare_weights
Figure 2. Snowshoe Hare weights for Males and Females. Range of weights for male and females during study period between 1999 and 2012.
# Calculate mean weight per year for males and females
avg_weight <- abundance_weights %>%
group_by(year, sex) %>%
summarize(
mean_weight = round(mean(weight), digits = 1),
sample = length(sex)
)
# Separate Male and Female into separate dataframes
mean_weight_female <- avg_weight %>%
filter(sex == "Female") %>%
select(year, mean_weight, sample) %>%
rename("Year" = year, "Mean Weight (g)" = mean_weight, "Count" = sample)
mean_weight_male <- avg_weight %>%
filter(sex == "Male") %>%
select(year, mean_weight, sample) %>%
rename("Year" = year, "Mean Weight (g)" = mean_weight, "Count" = sample)
# Merge male and female back together
weight_by_sex <- merge(mean_weight_female, mean_weight_male, by = "Year")
# Create kable table for mean weights
weights_table <-kable(weight_by_sex,
col.names = c("Year", "Mean Weight (g)", "Count", "Mean Weight (g)", "Count")) %>%
add_header_above(c(" " = 1, "Female" = 2, "Male" = 2)) %>%
kable_styling(bootstrap_options = c("striped", "hover"),
full_width = F,
position = "left",
fixed_thead = T
)
weights_table
| Year | Mean Weight (g) | Count | Mean Weight (g) | Count |
|---|---|---|---|---|
| 1998 | 1735.3 | 15 | 1646.7 | 18 |
| 1999 | 1295.4 | 163 | 1239.1 | 185 |
| 2000 | 1444.3 | 121 | 1300.5 | 107 |
| 2001 | 1437.8 | 38 | 1358.5 | 57 |
| 2002 | 1047.7 | 11 | 1301.5 | 17 |
| 2003 | 1205.4 | 34 | 1223.5 | 23 |
| 2004 | 1536.4 | 45 | 1372.4 | 29 |
| 2005 | 1232.3 | 103 | 1363.4 | 58 |
| 2006 | 1361.3 | 78 | 1486.4 | 33 |
| 2007 | 1426.9 | 132 | 1294.1 | 58 |
| 2008 | 1366.0 | 164 | 1395.9 | 133 |
| 2009 | 1352.2 | 247 | 1330.3 | 185 |
| 2010 | 1381.9 | 207 | 1428.1 | 113 |
| 2011 | 1380.2 | 129 | 1475.8 | 80 |
| 2012 | 1291.2 | 24 | 1331.0 | 21 |
Table 2. Mean Weight for Male and Female Snowshoe Hares (1999-2012). Mean weight for male and female hares for each year of the study period and count for each year. The highest mean weight for both males and females was during 1998.